1. Field of Invention
The present invention relates to a thin film transistor (TFT). More particularly, the present invention relates to a metal oxide TFT.
2. Description of Related Art
With advances in display technology and semiconductor processes, flat panel displays have been used in many kinds of electronic devices. A modern flat panel display has a thin film transistor (TFT) array substrate which is formed by a plurality of pixel units arranged in an array. Each pixel unit comprises a driving TFT and a switching TFT. The driving TFT is configured to drive a light-emitting element, and by switching on or off the switching TFT, image data can be stored in each pixel unit. Thus, the image quality of the flat panel display is largely dependent upon the performance of the TFTs therein.
FIG. 1 is a sectional view of a prior art TFT 100, in which the material of an active layer 140 of the TFT 100 is amorphous silicon. When a voltage larger than a threshold voltage of the TFT 100 is applied to a gate electrode 120, a channel is formed within the amorphous silicon active layer 140, causing the TFT 100 to be switched on. However, due to the low carrier density and carrier mobility in the amorphous silicon, both the orthographic projections of a source electrode 150 and a drain electrode 160 on a substrate 110, which are marked P1, P2 in FIG. 1, are required to overlap the gate electrode 120. Moreover, the low carrier density and carrier mobility in the amorphous silicon also limit the operating speed of the TFT 100, and therefore place limitations on the development of high-quality flat panel displays.
Thus, there is an urgent need to eliminate such defects.